The present invention relates to storage batteries, and more particularly to an explosion-proof battery vent and filler plug for stationary batteries.
In conventional storage batteries, the filling opening allows oxygen and hydrogen gases which form during the charging of the battery to escape from the battery. If this happens in the presence of a flame or spark, the hydrogen may be ignited, with the flame propagating back into the battery casing, causing explosion of the battery, which not only demolishes the battery and renders it incapable of further use, but may also cause severe personal injuries from the battery acid thrown about by the explosion. Also, the making of hydrometer tests to determine the state of charge of a battery may cause static electricity, resulting in a spark as the hydrometer enters the filling opening of the battery.
There have been various attempts to overcome these difficulties of conventional batteries. One such attempt is shown in U.S. Pat. No. 2,471,585, dated May 31, 1949, entitled "EXPLOSION-PROOF BATTERY VENT AND FILLER PLUG". There, the outer periphery of the filler plug is an annular screen made of a porous ceramic material, to provide a large area and low flow rate of escaping gases. A similar device is shown in U.S. Pat. No. 3,630,788, dated Dec. 28, 1971, entitled "VENTING AND FILLING DEVICE FOR STORAGE BATTERIES." There, two concentric, telescoping porous outer walls, generally tubular in shape, are shown, the outer wall telescoping over the inner wall to allow the positioning of a filling device to allow its use as a device for controlling the electrolyte level of a battery during filling.
These devices share a common deficiency. The provision of a large, porous escape area for gases evolved from the battery plates also provides a large escape area for fluid evaporating from the battery. The resulting need for frequent addition of water is a serious disadvantage, particularly in stationary batteries, which are designed for long-term stand-by use for emergency power supply, or for power leveling by utility companies, or for use with photovoltaic systems for powering unattended weather data collection instrumentation and unattended microwave radio repeater stations, particularly in sunny climates, where such systems are most desirable, but which also have high ambient temperatures. The resulting rate of evaporation at the least causes the necessity for the addition of water at intervals more frequently than desired, and may result in an insufficient electrolyte level, causing damage to the battery plate assembly if maintenance is omitted, or if a higher ambient temperature than usual causes an unanticipated rate of evaporation. Such damage may also result from temperatures caused by battery operation at a higher self-induced temperature than anticipated, such as when more frequent usage than anticipated is necessary. Such increased usage can be caused by, for instance, a series of clouds passing over a photovoltaic power supply, fewer sunny days than anticipated, or, in utility power leveling, hotter or cooler weather than anticipated, causing increased electrical use from increased use of heating or cooling devices.
As will be apparent, unexpected rates of electrolyte evaporation at such times may cause substantial and expensive damage to a large number of battery cells connected in a high-voltage, high current battery bank, causing at the very least a decrease in battery bank capacity and life.